Cut cling wrap into small squares. Scoop ½ teaspoon Nutella and ½ teaspoon of hazelnut spread onto individual cling-wrap squares. Fold to seal and freeze until solid.
In a large mixing bowl, add the cubed butter and whisk until slightly creamy. Add the white sugar and light brown sugar, then whisk together until well combined and fluffy.
Add the eggs and vanilla extract. Whisk until fully incorporated.
Add the flour, baking powder, baking soda, and salt. Gently mix until just combined, do not overmix.
Portion the dough into 65g-70g balls. Press a frozen Nutella hazelnut piece into the centre of each dough ball, seal well, and roll into a smooth ball.
Place the cookie dough balls onto a tray and freeze for at least 1 hour (or overnight for best results).
Preheat oven to 175-180°C (350°F). Bake for 10-15 minutes or until the tops are lightly golden while the centres remain soft.
Remove from the oven and let cool.
Melt the cooking or milk chocolate using double boiler method and add chopped and roasted hazelnuts to it.
Spread a layer of melted chocolate-hazelnut mixture onto baking paper, just enough to coat the base of the cookie. Gently place the cooled cookie on top, then spoon more of the mixture over it, making sure the cookie is fully covered and evenly coated.
Let the chocolate mixture set completely before serving.